Conventionally, there is a sheet treating apparatus for variously treating a sheet material such as an image forming apparatus for forming an image on a sheet material, image reading apparatus for reading an image on a sheet material or printed matter processing apparatus for classifying and processing printed matters such as bills. Sheet materials to be treated by the above sheet treating apparatus include not only plain paper, glossy paper, coated paper and film-like transparent resin sheet used for an image forming apparatus but also a printed matter such as a bill and various cards.
In this case, there is a sheet treating apparatus which has a sheet material identifying apparatus, identifies the kind of a sheet material by the sheet material identifying apparatus and then performs a treatment corresponding to the sheet material. For example, an image forming apparatus identifies the kind of a sheet material by a sheet material identifying apparatus and then controls a feed speed and a fixing temperature in accordance with the sheet material.
The kind of the sheet material is generally identified by using a difference between forces due to an electrical characteristic or contact friction of the sheet material. However, characteristics of a sheet material are changed due to humidity. Therefore, to identify the kind of the sheet material in accordance with the above method, a method is used in which the humidity in the sheet material identifying apparatus is measured to correct a value relating to the detected electrical characteristic and contact friction in accordance with the measured value (Japanese Patent Application Laid-Open No. 2002-139392).
In the case of the conventional sheet material identifying apparatus and sheet material identifying method, however, a shift may occur between the humidity of the sheet material identifying apparatus and that of a sheet material (that is, moisture content). When the shift is too large, a case is assumed in which the correction performed in accordance with the humidity in the sheet material identifying apparatus is not proper.
Moreover, when correction for the value relating to the electrical characteristic or contact friction thus detected is not properly performed, the sheet material may not be properly treated because the kind of the sheet material is not accurately identified. For example, in the case of an image forming apparatus, a feed speed or fixing temperature corresponding to the kind of a sheet material cannot be properly set and therefore, it may not be possible to form a proper image.